How to Prepare for a Radon Test at Home

A radon test is easy to schedule, but the conditions inside the home can affect whether the result reflects normal indoor exposure. Knowing how to prepare for a radon test helps prevent avoidable delays, repeat testing, and uncertainty during an already busy real estate transaction.

Radon is a naturally occurring radioactive gas that moves through soil and can enter a home through cracks, utility openings, sump pits, and other pathways in contact with the ground. It has no smell, color, or taste, so testing is the only practical way to know its level. In the Chicago area, radon can be a concern in homes with basements, crawlspaces, or slab foundations, regardless of age or construction quality.

How to Prepare for a Radon Test: Closed-House Conditions

Most real estate radon tests are short-term tests that run for at least 48 hours. For the results to be meaningful, the home should follow closed-house conditions for at least 12 hours before the test begins and throughout the testing period.

In practical terms, keep windows closed and do not leave exterior doors open. Family members may enter and leave the home normally, but avoid propping doors open for moving, deliveries, pets, contractors, or ventilation. A brief trip in and out will not ruin a test. Repeated or extended opening of doors and windows can change indoor air pressure and dilute radon levels.

Keep the heating and air conditioning systems operating normally. The goal is not to create unusual conditions, but to measure the home as it is typically lived in. If the home is usually heated during a Chicago winter or air conditioned during summer, continue using those systems as usual.

What “closed” does and does not mean

Closed-house conditions do not mean the home must be empty or uncomfortable. You can cook, shower, use bathrooms, and go about regular daily activities. You should not open windows to air out the house, run window fans, or operate a whole-house fan that brings large amounts of outdoor air inside.

If there is a window air conditioner, keep its outdoor-air vent closed if it has one. Portable air conditioners and dehumidifiers can generally operate as they normally would, unless the testing professional gives different instructions. The key is to avoid intentional ventilation that changes the air exchange between indoors and outdoors.

Avoid Changes That Can Interfere With Results

A radon measurement is most useful when it represents the home's ordinary conditions. Major changes during the test can make the result harder to interpret.

Do not begin a renovation project, open basement windows for painting or cleaning, or schedule work that requires exterior doors to remain open. Avoid pressure washing, foundation work, and similar projects around the house while the test is underway. If a contractor must access the home, let the testing professional know before the test begins so the schedule can be adjusted if needed.

Fireplaces and wood-burning stoves deserve some extra thought. If you do not normally use one, do not light it during the testing period. If it is part of the household's normal heating routine, ask the inspector how to proceed. Combustion appliances and exhaust systems can affect air movement in a home, so consistency matters more than trying to create idealized conditions.

Do not cover, unplug, move, or place objects around the testing device. Continuous radon monitors often record hourly readings as well as conditions that may indicate tampering or unusual test circumstances. The device should stay where it was placed until the inspector returns to retrieve it.

Prepare the Test Area for Access

The inspector will select the appropriate testing location, usually the lowest level of the home that could be regularly occupied. That may be a basement, lower-level family room, or main floor in a home without a basement. The device is not normally placed in a crawlspace, kitchen, bathroom, laundry room, or other area where humidity, drafts, or frequent activity could affect the reading.

Before the appointment, make sure the inspector can access the lower level and any area that may need to be evaluated. Clear a reasonable path through storage, move pets away from the work area, and make sure the home can be secured after the device is placed. There is no need to rearrange the entire basement. Simple, safe access is usually enough.

If the home is vacant, confirm that utilities are on and that the HVAC system can operate normally. A vacant home with open windows, disconnected heat, or inconsistent conditions may need additional preparation before testing can begin.

If the home has a sump pit or existing mitigation system

A sump pit is a common radon entry point, especially in homes with basements. Do not attempt to seal, modify, or repair it immediately before a test unless that work is part of a planned radon mitigation project. Making last-minute changes can prevent the test from showing the conditions a buyer or homeowner needs to understand.

If the home already has a radon mitigation system, it should generally remain operating during a standard radon test. Turning it off may create an artificially high result and does not show whether the system is doing its job. The exception is diagnostic testing requested specifically to evaluate a system or determine its impact. In that case, follow the radon professional's instructions exactly.

Planning Around a Home Sale

For buyers and sellers, timing is often the biggest challenge. A 48-hour test needs a period when the property can remain under closed-house conditions. Coordinate with the real estate agent, occupants, and any contractors before the device is placed.

Sellers can make the process easier by sharing the test instructions with everyone who has access to the home. A cleaner, showing agent, family member, or contractor may open windows with good intentions, not realizing the test is in progress. A simple note on the thermostat or near the main exit can help: radon test underway, please keep windows closed and do not move the monitor.

Buyers should understand that a radon result is not a pass-or-fail grade for the entire property. It is a measurement of radon concentration during a specific test period. Weather, soil moisture, heating patterns, and pressure differences can cause levels to vary over time. That is why professional testing methods and proper test conditions matter.

When a short-term result is at or above 4.0 picocuries per liter, the commonly used action level, the next step is usually to discuss mitigation or, in some situations, confirmatory testing. A qualified mitigation professional can design a system based on the home's foundation type and radon entry pathways. Many homes can be effectively mitigated without disrupting normal use of the property.

Common Mistakes to Avoid Before a Radon Test

The most frequent problem is opening windows because the weather is pleasant or the house feels stuffy. Another is forgetting about a planned service appointment that requires a door to stay open. Neither mistake means the home has a radon issue, but either can compromise the testing conditions and require the test to be repeated.

It is also a mistake to assume a neighbor's result predicts yours. Two homes on the same street can have very different radon levels because of differences in foundation construction, soil contact, drainage, and air pressure. A new home can have radon, and a well-maintained home can have radon. Testing your specific property is the dependable answer.

Finally, do not try to influence the outcome by opening windows, shutting down a mitigation fan, or making unusual HVAC changes. Reliable information protects everyone in a transaction. It gives buyers a clearer understanding of the home and gives sellers a defined issue to address rather than an unresolved question after closing.

A Simple Checklist Before the Monitor Is Placed

At least 12 hours before the appointment, close windows and keep exterior doors closed except for normal entry and exit. Keep heating or cooling on as usual, postpone projects that require prolonged ventilation, and make sure the lower level is accessible. During the test, leave the monitor alone and continue normal daily life without intentional fresh-air ventilation.

A careful radon test does more than produce a number. It gives you dependable information for a safer, more informed decision about the home. If you are unsure whether a planned activity could affect the test, ask before the monitor is placed. A quick question can protect the value of the entire testing process.